The problem with waiting is that chances are, there will be even better ones than whatever you are waiting for now, eventually, should you wait for that too?

Also, some player hypnosis, overly optimistically if you ask me but not impossible, that new tools would also come with better secondary stat, at least on par with red gourd and possibly better. This would defeat the purpose of some of the tool essence. And as long as they aren't selling tool essence, and ergo this would not impact their income, this remains possible. If they do start selling tool essence thou, we can be fairly certain that new tools wont have good stat as that would cause them to lose income.

And besides, if they release multiple red for each slot, and you forge up the best ones among those, there is the chance that, like they did to the gold, where they nerf those ones such that the best ones change, nullifying your effort.

As it stands, the game doesn't have a very good track record as far as ninja tools goes in terms of consistency, so whether waiting is.... questionable at best.

So personally, I think while it might be worth while to keep the most valuable ones, which is nin/tai, rest can be used as the benefit of waiting is unclear.